Story drift Δ is the difference between lateral deflections at each story level above and below the story you are checking.

The deflection at story x equals:

δx = Cd ( δxe) / I(E)

Cd is your magnification factor in table 1617.6

δxe is the deflection of the floor level based on an elastic, first order analysis using the seismic design loads on the entire structure.

I(E) is simply the occupancy importance factor.

So once you calculate the δ at each floor, take them times Cd and divide by I(E), you have a δx at each floor.  Their difference is the Δ for each story which compares with the allowable story drifts in table 1617.3